1. Field of the Invention
The present invention is in the field of denture retention. More specifically, the present invention is directed to a connector-support structure which with or without magnets anchors overdentures to implant fixtures which are themselves embedded within the jaw bone or tooth root of a person, and cushions the bone or tooth root from masticatory force loads generated by the dentures.
2. Brief Description of the Prior Art
Implant fixtures embedded in the jaw bone or in the tooth root, and connectors removably mounted to the implant fixtures, to provide support for complete and partial dentures are known in the prior art. The dentures, which include one or more false teeth, are affixed, usually in a removable manner, to the connectors. There is a relatively large number of United States and foreign patent disclosures, articles and publications which describe various ways for affixing the overlying dentures to the underlying implant fixtures.
More specifically, the following United States and foreign patents, articles and publications describe various structures wherein magnets are employed to attach the removable dentures to the bone- or tooth root embedded implants: U.S. Pat. Nos. 4,508,507, 4,431,419, 4,626,213, 4,209,905, 4,184,252, 4,214,366, Australian Provisional Patent Specification titled "Magnet Structure" by A. R. Gillings, French Patent Nos. 73.12280 and 75 12748, German Published Patent Application No. 2201415, an article titled "Retentive characteristics of different magnetic systems for dental applications" by Ron Highton et al. in THE JOURNAL OF PROSTHETIC DENTISTRY Volume 56 pp 104-106, Jul. 1986, an article titled "A magnetic attachment for overdentures" by H. Sasaki et al. in THE JOURNAL OF PROSTHETIC DENTISTRY Volume 51 pp 450-455 (1984), a publication titled "THE USE OF RARE EARTH MAGNETIC ASSEMBLIES FOR RETENTION OF DENTAL PROSTHETICS" by T. R. Jackson and a publication titled "MAGNETIC RETENTION UNITS FOR OVERLAY DENTURES" BY B. R. D. Gillings.
U.S. Pat. No. 3,787,975, describes a bone or root canal embedded implant which utilizes a mechanical device, including a socket and a matching ball, for removably attaching the denture to the anchor. A device of related construction, well known in the art under the trade name ZEST of Zest Anchors Inc. of San Diego, Calif., uses a bone or tooth root embedded implant fixture, a connector having a transmucosal cuff including an interior socket, and a keeper member having a ball which fits into the socket, for retaining dentures in the patient's mouth. The keeper member utilizes a strong permanent magnet in the denture to hold the denture.
Other references related to dental prostheses or tissue integrated prostheses include U.S. Pat. Nos. 4,261,350, 4,330,891, British Patent Specification No. 1291 470 and the article titled "BIOPHYSIKALISCHER BEITRAG ZUR PROBLEMATIK STARR ABGESTUTZTER FREIENDPROTHESEN" by H. Rehm at al., DZZ 17 1962 pp 963-975.
It has been recognized in the prior art, that mastication (chewing) subjects a person's teeth, underlying tooth roots, tissue and bone structure to significant forces. Normal, healthy teeth and tissue structure are capable of resiliently yielding under the masticatory forces, and accommodate and absorb these forces without harmful effect. For artificial teeth, and for the underlying implanted fixtures and bone structure, the masticatory forces, however, present a significant problem, and often cause patient discomfort and deterioration of the fixation of the implant fixture in the bone or in the tooth root.
The following articles, publications discuss the nature and magnitude of masticatory forces and their effect on dental prostheses: "Tissue-Integrated Prosthesis" by Branemark/Zarb/Albrektsson (Quintessence Books) pages 123-128; "The Bar Joint Denture" by E. Dolder and G. T. Durrer (Quintessence Books) 1978, pages 95-102; "Precision Work for Partial dentures" by A. Steiger et al. pages 143-145. The last mentioned publication discloses that a healthy human tooth has a resiliency of approximately 0.1 mm in its socket, and that healthy mucous tissue provides a resiliency of approximately 4 to 20 times greater than the resiliency of the tooth in the socket. Conventional rigid prosthetic dental structures, on the other hand, provide virtually zero resiliency.
In fact, and in sharp contrast with the resiliency of natural healthy teeth, there have only been ineffectual attempts in the prior art to provide a limited degree of freedom of motion and force absorbing capability to dental prosthetic structures.
For example, the prior art device known in the art under the ZEST name employs a socket and ball type attachment of the dentures to the underlying implant fixture. By its nature, the socket and ball joint provides a slight degree of freedom of motion and a slight degree of vertical resiliency.
A publication titled "Stress Absorbing Elements in Implants" prepared by Core-Vent Corporation of Encino, Calif., discusses stress absorption in dental prostheses by using plastic screws in the "anchoring" structures, and by the use of intermediate plastic (polyoxymethylene, DELRIN) connector plates such as employed by an IMZ dental implant system and distributed by Interpore International of Irvine, Calif. This publication actually expresses doubt regarding the practical utility of these prior art attempts to provide resiliency to dental prostheses.
In light of the foregoing, there is a need in the prior art for connectors or anchors for dental prostheses, which have significant ability to absorb masticatory forces, and provide a desirable freedom of motion to the prostheses. The present invention satisfies this need.